Sensors are widely used in modern systems to measure or detect physical parameters, such as position, motion, force, acceleration, temperature, pressure, etc. While a variety of different sensor types exist for measuring these and other parameters, they all suffer from various limitations. For example, inexpensive low field sensors, such as those used in an electronic compass and other similar magnetic sensing applications, generally are anisotropic magnetoresistance (AMR) based devices. In order to arrive at the required sensitivity and reasonable resistances that mesh well with CMOS, the sensing units of such sensors are generally on the order of square millimeters in size. For mobile applications, such AMR sensor configurations are too costly, in terms of expense, circuit area, and power consumption.
Other types of sensors, such as magnetic tunnel junction (MTJ) sensors and giant magnetoresistance (GMR) sensors, have been used to provide smaller profile sensors, but such sensors have their own concerns, such as inadequate sensitivity and being affected by temperature changes. To address these concerns, MTJ, GMR, and AMR sensors have been employed in a Wheatstone bridge structure to increase sensitivity and to eliminate temperature dependent resistance changes. For minimal sensor size and cost, MTJ or GMR elements are preferred. Typically, a Wheatstone bridge structure uses magnetic shields to suppress the response of reference elements within the bridge so that only the sense elements (and hence the bridge) respond in a predetermined manner. However, the magnetic shields are thick and their fabrication requires carefully tuned NiFe seed and plating steps. Another drawback associated with magnetic shields arises when the shield retains a remnant field when exposed to a strong (˜5 kOe) magnetic field, since this remnant field can impair the low field measuring capabilities of the bridge structure. To prevent the use of magnetic shields and to sense an external magnetic in three axis (X, Y, Z), three Wheatstone bridge structures (one for each axis) are used. The layers of each bridge structure are fabricated in the same processes in similar layers. In order to sense the magnetic field in the Z axis, flux guides are used to guide the Z axis field into the X-Y plane to be sensed by one of the bridge structures. These flux guides have a preferred magnetization orientation for optimal Z axis response. Exposure to a very large external field in a particular orientation can reorient the flux guide magnetization so that upon returning to its low field sensing configuration, magnetic domain walls may be present in the Z axis flux guides. The tiny fluctuations in the dipolar field at the sense element generated by temperature induced motion of these domain walls along the flux guide length can elevate the overall sensor noise above the lowest achievable output noise, and reduce signal to noise ratio (SNR).
Accordingly, a need exists for an improved design and fabrication process for forming a single chip magnetic sensor that is responsive an applied magnetic field in three dimensions in which magnetic domain walls in the Z axis flux guides may be eliminated, should the sensor be exposed to a large magnetic field. There is also a need for a three-axis sensor that can be efficiently and inexpensively constructed as an integrated circuit structure for use in mobile applications. There is also a need for an improved magnetic field sensor and fabrication to overcome the problems in the art, such as outlined above. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background.